Battery charging with auxilliary engine

[gpl]

I wasn't sure whether "Electronics" would have been the right category but here it goes.

My main engine is a Suzuki DF 175 charging two 12V/80Ah batteries via its twin alternator output. My auxiliary is a 2004 Mercury F8ELH which does have a small (? 30 W) alternator. I would like to use this to recharge the domestic battery during long hours of trolling, when GPS/Sonar/VHF/ stereo seem to drain a lot of juice (around 2.5+ AH/h).
The dealer said the output from the Mercury is "dirty" and could cause damage to the electronics. Is this so? If not what would be the way to set this up? I am considering the alternative of a 45W solar panel
Any advice would be greatly appreciated!
Many thanks in advance

[ian parkes]

if my crap electrical knowlege is right you would have over 30 hrs on one battery alone , thats a lot of trolling .

If i don't catch anything after an hour i give up

[codprawn]

Ian is right - just don't drain your starter battery.

As to the dirty output of the small outboard it isn't a problem if it is also charging the batteries. They only cause trouble if you have no battery to charge and try to run things straight off the motor.

Batteries are great for smoothing current - they don't bother regulating small alternators as they know the battery will do it for them!!!

[doggypaddle]

I agree with that, the battery will act as both a smoothing capacitor and shunt regulator for a small alternator putting out 30watts. you need to remember that the 30 watts is rated probably at max RPM, at half revs the output may well be less, if you have a 110 ah battery probably not even worth bothering? most of the time it will output 1amp.
because they arent regulated the open circuit voltage and hence the imedance of the circuit is quite high, this means the charge rate is dependent on engine rpm and not so much battery state of charge. The opposite is true of regulated and typically larger alternators.

[gpl]

Thanks everyone for the feedback!

Ian

If i don't catch anything after an hour i give up

Don't I know the feeling!

I should have clarified though, this is trolling along a beautiful Greek island coastline, sipping cool drinks, and relaxing, so quite prepared to suffer in silence for a bit longer!

Now, the problem occurs when you spent more than a few days there, since you are not really operating the main engine for any period of time sufficient to recharge. Add to this a downrigger and the problem is complicated further.

I do take the points though. Probably a Solar panel with a MPPT black box is the way to go.

[ian parkes]

Greece maybe the solar panel isn't a bad idea .

I hope the marine life isn't as disapointing there as it was in cyprus , I was expecting to see lots of fish there but the place seemed to be dead exept for a few tiny little fish even the seaweed looked dead .

[gpl]

A lot depends on the particular spot but overall there's still enough to keep me happy during my summer holidays.

Cyprus, I can't really tell, but as you know a place that looks dead one day may be breaming with fish the next... Moon, wind, current, time of day, its all a mystery to me.

http://img176.imageshack.us/my.php?i...ddaych7rs2.jpg

[willk]

gpl - what a photo! Whatever the costs of running a RIB, that's gotta make it all worth it.

[gpl]

willk